125 patients with primary knee osteoarthritis from 4 participating sites who meet inclusion/exclusion criteria will be enrolled into the trial. After initial screening, patients will attend clinic for baseline examination. Subjects will then randomly allocated to periarticular parecoxib sodium or intravenous sodium in ratio of 1:1. patients are observed at post-operative 6, 12, 24 hours, subsequently daily for 4 days and finally at 2 week follow-up